What Are the Effects of Low Progesterone Levels in Pregnancy?

Progesterone is a hormone released by the female body after ovulation, and it remains in elevated levels throughout a healthy pregnancy. When a woman's progesterone levels are low in early pregnancy, supplements may be needed to prevent a miscarriage, because progesterone is necessary to help the fetus develop. Light vaginal bleeding, often called spotting, is one common sign of low progesterone levels in pregnancy, and this symptom often precedes a miscarriage. Pregnant women who suspect problems with their progesterone levels can ask their doctor to test their levels and prescribe progesterone supplementation, if necessary.

The corpus luteum produces progesterone after ovulation to thicken the uterus in preparation for pregnancy. If there is no pregnancy, progesterone levels decrease and the thick uterine lining sheds during menstruation. When a pregnancy does occur, the levels increase, but the job of progesterone production is assumed by the placenta around the 10th week of pregnancy. Healthy progesterone levels in pregnancy allow the fetus to develop and also keep blood circulating properly through the uterus. In addition, this hormone can stop the body from treating the embryo as a foreign object and can stop uterine contractions, both reasons why low levels can result in miscarriage.

A low progesterone level is often considered one of the most common causes of an early miscarriage. The typical sign of an impending miscarriage is light bleeding, or spotting, in which light pink or brown blood appears in the underwear or on the toilet paper when wiping after urinating. When spotting is accompanied by severe cramps and loss of the typical pregnancy symptoms, women are encouraged to call their doctor to check on the viability of the pregnancy. Spotting is often caused by some of the uterine lining shedding as a result of decreased progesterone levels, which can make it difficult for an embryo to implant and lead to a miscarriage. In some cases, spotting can occur without a miscarriage and the progesterone level may be just enough to continue the pregnancy as normal.

Women who are worried about low progesterone levels in pregnancy can request a test from their doctor. This usually involves a blood test and the results are typically available within a day. If the level is low, some doctors offer progesterone injections, pills or suppositories to help prevent early miscarriage. Not every doctor recommends testing or treating low progesterone levels in pregnancy, though, because many in the medical community say supplementation has little effect on the potential for miscarriage. Their theory is that a decreased level of this hormone is an indication that a miscarriage may occur for other reasons, such as a chromosomal abnormality, rather than the decrease being the cause.